In the past data acquisition systems have typically had a fixed number of input lines for receiving signals and a fixed number of output lines for providing either electrical current or voltage to sensors or other apparatus from which data is to be acquired. Furthermore, in typical prior art systems a signal input line must be designated to receive either a digital signal or an analog signal when the data acquisition system is constructed.
In modular systems a data acquisition system may be desired to be connected to different types of sensors on different occasions. Some of these sensors will require a voltage reference while others will require a current reference. Also, some of these sensors will provide a digital output while others will provide an analog output. A data acquisition system which could provide varying combinations of electrical current and voltages to the sensors to be monitored and receive varying combinations of digital and analog signals would be desirable.